The BBX family of plant transcription factors

• B-box (BBX) transcription factors are a conserved group of proteins with a zinc-binding B-Box-domain.
• BBX proteins are involved in transcriptional activity and protein–protein interaction.
• BBX proteins are cofactors that control growth and development throughout the plant life cycle.
• Different members of the BBX protein family can play opposite roles in the same physiological processes.

The B-box (BBX) proteins are a class of zinc-finger transcription factors containing a B-box domain with one or two B-box motifs, and sometimes also feature a CCT (CONSTANS, CO-like, and TOC1) domain. BBX proteins are key factors in regulatory networks controlling growth and developmental processes that include seedling photomorphogenesis, photoperiodic regulation of flowering, shade avoidance, and responses to biotic and abiotic stresses. In this review we discuss the functions of BBX proteins and the role of B-box motif in mediating transcriptional regulation and protein–protein interaction in plant signaling. In addition, we provide novel insights into the molecular mechanisms of their action and the evolutionary significance of their functional divergence.